A. Neovascularization
Neovascularization (or angiogenesis) is a process whereby new blood vessels are formed within tissues of the body. Normal neovascularization is the physiological process by which the body creates and maintains small blood vessels of the circulatory system. However, pathological or latrogenic neovascularization is a non-physiological process whereby abnormal networks of blood vessels are created in tissues of the body or in tumors, as a result of certain diseases, trauma or surgical procedures.
Pathological neovascularization occur within tissues of the eye as a result of certain ophthalmic disorders such as diabetic retinopathies, proliferative vitreo-retinopathies, corneal neovascularization, iris rubeosis, and diseases that cause ischemia of the ocular tissues (e.g., occlusion of the central retinal vein, occlusion of the central retinal artery, certain inflammatory conditions, etc.). Also, iatrogenic neovascularization can occur following certain ophthalmological surgical procedures which disrupt normal blood supply to tissues of the eye or those which cause localized proliferations of cells known as “fibroblasts”. Examples of ophthalmological surgical procedured that have been associated with untoward post-surgical neovascularization include glaucoma filtration surgery and corneal transplant surgery.
Various types of drugs and agents (e.g., steroids, non-steroidal anti-inflammatory drugs (NSAIDS), heparin, protamine, calcitrol, antibiotics, thrombospodin fragments, and monodonal antibodies directed to fibroblast growth factor) have been purported to be useable to treat or prevent neovascularization of the anterior segment of the eye. Non steriodal anti-inflammatory drugs have not been used to treat neovascularization of the posterior segment of the eye.
Also, laser surgical procedures have been used to ablate or destroy neo-vascular networks which develop in the retina or epiretinal membranes. However, these prior therapies for ocular neovascularization have been less than completely effective and/or have been associated with side effects. For example, glucocorticoids and other angiostatic steroids have been used to treat neovascularization of the anterior chamber (e.g., corneal neovascularization, iris rubeosis) and/or other ocular tissues, but such steroid treatments have been associated with side effects such as elevated intraoccular pressure. see, Kitazawa, Increased Intraocular Pressure Induced by Corticosteroids, American Journal of Ophthalmology, Vol. 82, Pg.492-493 (1976).
B. Intravitreal Hemorrhage and the Need for Liquefaction of the Vitreous Body and/or Posterior Vitreous Dissinsertion or Detachment Prior to Vitrectomy:
In many mammals including human beings, the “vitreous body” is disposed within a posterior portion of the eye and occupies approximately four fifths of the cavity of the eyeball, behind the lens. The vitreous body is formed of gelatinous material, known as the vitreous humor. The vitreous humor of a normal human eye is made up of approximately 99% water along with 1% macromolecules including; collagen, hyaluronic acid, soluble glycoproteins, sugars and other low molecular weight metabolites.
The retina is essentially a layer of nervous tissue which covers a portion of the inner wall of the posterior segment—in juxtaposition to the posterior aspect of the vitreous body. The retina is surrounded by a layer of cells known as the choroid layer. The retina may be divided into a) an optic portion which participates in the visual mechanism, and b) a non-optic portion which does not participate in the visual mechanism. The optic portion of the retina contains the rods and cones, which are the effectual organs of vision. A number of arteries and veins enter the retina at its center, and splay outwardly to provide blood circulation to the retina.
The posterior portion of the vitreous body is in direct contact with the retina. Networks of fibrillar strands extend from the retina and permeate or insert into the vitreous body so as to attach the vitreous body to the retina.
Diabetic retinopathy, trauma and other ophthalmological disorders sometimes result in rupture or leakage of retinal blood vessels with resultant bleeding into the vitreous humor of the eye (i.e., “intravitreal hemorrhage). Such intravitreal hemorrhage typically manifests as clouding or opacification of the vitreous humor.
Intravitreal hemorrhage is sometimes, but not always, accompanied by tearing or detachment of the retina. In cases where the intravitreal hemorrhage is accompanied by a retinal tear or detachment, it is important that such retinal tear or detachment be promptly diagnosed and surgically repaired. Failure to promptly diagnose and repair the retinal tear or detachment may allow photo-receptor cells of the retina, in the region of the tear or detachment, to become necrotic. Such necrosis of the photoreceptor cells of the retina may result in loss of vision. Furthermore, allowing the retinal detachment to remain unrepaired for such extended period of time may result in further intravitreal hemorrhage and/or the formation of fibrous tissue at the site of the hemorrhage. Such formation of fibrous tissue may result in the formation of an undesirable fibrous attachment between the vitreous body and the retina.
The typical surgical procedure used for repair of retinal tears or detachment requires that the surgeon be able to look through the vitreous humor, to visualize the damaged region of the retina (i.e., “transvitreous viewing of the retina”). When intravitreal hemorrhage has occurred, the presence of the hemorrhagic blood within the vitreous can cause the vitreous to become so cloudy that the surgeon is prevented from visualizing the retina through the vitreous. Such hemorrhagic clouding of the vitreous can take 6-12 months or longer to clear sufficiently to permit trans-vitreal viewing of the retina. However, in view of the potential complications which may result from delayed diagnosis or treatment of a retinal tear or detachment, it is generally not desirable to wait for such natural clearance of the hemorrhagic blood to occur.
Furthermore, even when the intravitreal hemorrhage is not accompanied by retinal tear or detachment, it is often difficult to verify that retinal tear or detachment has not occurred, because the hemorrhagic clouding of the vitreous prevents the physician from performing routine funduscopic examination of the retina. Moreover, the presence of hemorrhagic blood within the vitreous may significantly impair the patient's vision through the affected eye, and will continue to do so until such time as the hemorrhagic blood has been substantially or fully cleared.
Thus, the presence of hemorrhagic blood within the vitreous body causes multiple clinical problems including a) inability to visually examine and diagnose the site of the hemorrhage and/or any accompanying tear or detachment of the retina, b) full or partial impairment of vision in the affected eye and c) impairment or prevention of the performance of trans-vitreal surgical procedures of the type typically utilized to repair the site of hemorrhage and/or to repair any accompanying retinal tear or detachment. In cases where intravitreal hemorrhage has resulted in substantial clouding or opacification of the vitreous, the treating physician may have the option to perform a procedure known as a vitrectomy, wherein all (or a portion of) the vitreous body is removed from the interior of the eye, and replaced with a clear liquid or gas. The performance of such vitrectomy procedure is intended to allow the surgeon to visualize the retina sufficiently to proceed with the necessary retinal examination and/or surgical repair of the hemorrhage and any accompanying retinal tear or detachment. However, such vitrectomy procedures are highly skill-intensive, and are associated with several significant drawbacks, risks and complications. Among these drawbacks, risks and complications are the potential that the act of removing the vitreous will cause further detachment or tearing of the retina and/or that such removal of the vitreous will cause further hemorrhage from the already-weakened retinal blood vessels. In order to minimize the stress of tugging on the retina during vitrectomy and to otherwise facilitate the removal of the vitreous body, it is sometimes desirable to precede the vitrectomy by the intravitreal injection of a substance which will cause liquefaction of the vitreous humor and/or disinsertion/detachment of the vitreous humor from the adjacent tissues of the retina and epiretinal membranes. Examples of substances which have been purported to cause vitreal liquefaction and/or posterior vitreous detachmentdisinsertion are found in U.S. Pat. No. 4,820,516 (Sawyer), U.S. Pat. No. 5,292,509 (Hageman) and U.S. Pat. No. 5,866,120 (Karageozian et al.).
C. Prior Ophthalmic Applications of Urea and Urea Derivatives:
U.S. Pat. No. 5,629,344 (Charlton et al.) has described the topical application to the cornea or “surface” of the eye of urea and/or urea derivative(s) to treat ocular conditions such as dryness, non-infectious keratitis, irregularities of the corneal or conjunctival epithelium, ocular scarring and “subjective irritations” as well as to inhibit unwanted fibroblast formation and/or enhance healing following glaucoma, cataract and corneal surgeries.
D. Prior Ophthalmic Applications of Non-Steroidal Anti-Inflammatory Agents:
Several NSAIDS have heretofore been known for oral administration and/or topical application to the eye for the purpose of treating inflammatory conditions of the eye and/or post surgical pain and inflamation of the anterior segment of the eye. Examples of NSAIDS that are presently available for topical application to the eye include diclofenac (Cataflam), flurbiprofen (Ansaid), ketorolac (Toradol, Acular). To date, ophthalmic NSAID preparations have been used primarily to treat inflammatory disorders of the cornea and anterior segment of the eye. In instances where ophthalmic NSAIDS have been administered to treat disorders of the posterior segment of the eye, the NSAID has been Initially applied to the anterior segment of the eye with the intention that a therapeutic amount of the NSAID will distribute from the anterior segment to the posterior segment of the eye where the therapeutic effect is desired. For example, Acular™ (ketorolac) drops have been applied topically to the anterior segment of the eye (i.e., to the cornea) for the purpose of treating cystoid macular edema—a disorder of the posterior segment of the eye.
E. Prior Ophthalmic Applications of Anti-Metabolites:
5-Fluorouracil and Mitomicin C have previously been purported to be useable, when administered to the anterior segment of the eye, to inhibit or treat certain conditions of the anterior segment that are characterized by undesired tissue proliferation such as benign fibrovascular lesions of the conjunctiva known as Pterygia.